1. Field of the Invention
The present invention relates to an internal combustion engine using a fuel containing hydrocarbons.
2. Description of the Related Art
In recent years, in internal combustion engines using a fuel containing hydrocarbons, employing of the homogeneous charge compression ignition system has been studied to reduce the emission amount of pollutants such as NOx and soot. Internal combustion engines using the homogeneous charge compression ignition system involve preliminarily mixing a fuel and air, and compressing the obtained fuel-air mixture to self-ignition. If an internal combustion engine using the homogeneous charge compression ignition system is used, since a homogeneous dilute fuel-air mixture is made to burn, the combustion temperature does not become high, and the generation amount of NOx can be suppressed low; and since the fuel-air mixture burns homogeneously in a combustion chamber, the generation amount of soot can be suppressed low.
However, in internal combustion engines using the homogeneous charge compression ignition system, since the ignition timing is determined according to the temperature and the pressure in the combustion chamber, the ignition control is difficult, raising a problem of the engines being able to be stably operated only under a low or medium load, at a low or medium rotation.
By contrast, in internal combustion engines using the spark ignition system, since a fuel-air mixture in a combustion chamber is ignited by a spark, if a timing to generate a spark is suitably set, the fuel-air mixture can surely be made to burn, and the engines can be stably operated even under a high load, at a high rotation. So, an internal combustion engine is proposed which operates by either the homogeneous charge compression ignition system or the spark ignition system depending on its load (for example, seeing Japanese Patent Laid-Open No. 2004-150383)
However, since although the homogeneous charge compression ignition system requires a fuel having a high ignitability, the spark ignition system requires a fuel having a low ignitability, there exists an inconvenience that it is difficult to operate by either the homogeneous charge compression ignition system or the spark ignition system in an internal combustion engine with a single fuel.